text: #!/afs/bx.psu.edu/project/pythons/py2.7-linux-x86_64-ucs2/bin/python2.7
  
  """
  Read a maf from stdin and print the chromosome number for each alignment. It
  searches for 'chr' in each alignment block src, and may not be robust if other
  src formats are used. 
  
  NOTE: See 'align_print_template.py' for a more general variation of this
        program.
  
  usage: %prog refindex [options]
  """
  
  from __future__ import division
  
  import sys
  from bx.cookbook import doc_optparse
  from bx.align import maf
  from optparse import OptionParser
  
  def __main__():
  
      # Parse command line arguments
      options, args = doc_optparse.parse( __doc__ )
  
      try:
          refindex = int( args[0] )
      except:
          doc_optparse.exit()
  
      maf_reader = maf.Reader( sys.stdin )
  
      for m in maf_reader: 
  		c = m.components[ refindex ].src
  		print c[ c.rfind( "chr" ) + 3 : ]
  
  if __name__ == "__main__": __main__()
  